Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A typical image forming apparatus, such as a printer-only machine and a Multifunction Peripheral (MFP), has an input/output property that changes due to a cause such as a secular change. There is a known calibration method performing a correction of, so-called gamma correction, measuring a spectral reflectance of a patch included in a patch chart to obtain a correction value by using an integral sum of differences between the measured spectral reflectance and an ideal spectral reflectance.